1. Field of the Invention
The present invention relates to an aluminum alloy used to manufacture tubular elements or other members of heat exchangers such as those incorporated in radiators, car heaters, intercoolers or the likes.
2. Description of the Prior Art
The aluminum alloy "A3003" has been used in general to manufacture structural elements such as the tubular elements which allow a heat exchanging medium to flow therethrough, because the alloy "A3003" is easy to treat in the manufacturing processes.
Higher contents of impurities such as iron (Fe) in the aluminum alloy A3003 cause inferior corrosion resistance thereof at room temperature or near temperatures close thereto. Efforts have been made to improve the corrosion resistance at such lower temperatures, by making the impurity contents as low as possible. However in this case, there arises a new problem that intercrystalline corrosion takes place at higher temperatures including 100.degree. C., i.e., the boiling temperature of water and near temperatures close thereto. Corrosion of such a type causes cracks in the tubular elements.
In view of those problems and particularly in a case in which water or other corrosive heat-exchanging medium is likely to be employed for the heat exchangers in radiators or the likes, tubes of aluminum alloy A3003 are used as "cores" of tubular elements and their inner surfaces are covered with a lining layer of another aluminum alloy such as "A7072" or "A5005". The alloy A7072 functions as a sacrificial anodic layer, and the other alloy A5005 is comparatively highly corrosion-resistant.
These aluminum alloys A7075 and A5005 used as the lining layer are also not satisfactory because their corrosion resistance becomes worse at or near room temperature with a rich content of Fe, and because a lower Fe content reduced to improve the corrosion resistance at lower temperatures will give rise to the problem of intercrystalline corrosion at higher temperature of or near 100.degree. C.
There has been still another problem that the mechanical strength is often lowered for instance to about 4 Kgf/mm.sup.2 as a value of .sigma.0.2 ( tolerable load ) after the structural members of heat exchangers made of the alloy "A3003" are soldered to each other. Thus, walls constituting the tubular elements or other members are to be inevitably made thicker to assure sufficient strength thereof. Therefore, manufacturers have inevitably had to accept a larger size, an excessive weight and a higher manufacture cost of the known heat exchangers. The abovementioned problems have occurred not only in the tubular elements but also in the other structural members of heat exchangers made of such aluminum alloys.